Embryo Quality and Grading: What Does an Embryo Grade Mean and What Does It Not Show?

Embryo quality is the assessment and grading of the embryo in the IVF laboratory under the microscope according to certain criteria. The embryologist looks, according to the stage of development, at the number of cells, how alike the cells are to one another and their appearance; at the blastocyst stage, a grade is given with a code made up of letters and numbers. This grade gives partial information about your embryo, based on probability. A high grade does not mean pregnancy; a low grade does not determine the outcome either. Nor does the grade show that the embryo's chromosomes are normal; understanding this is the job of genetic tests. This text is for general information; consult your doctor and embryologist to interpret the grade of your own embryos.

What is embryo quality, and how is it assessed?

The current expert guideline on this subject aims to bring the terms and criteria used in the microscopic assessment of the egg and embryo into a common language. According to this guideline, "grading" is the process of giving the embryo a quality grade. "Ranking and selection", which determines which embryo will be transferred, is a separate concept and includes other factors besides grading.

What does the embryologist look at in your embryo?

The assessment is made according to the stage the embryo has reached that day. In an embryo at the cleavage stage, the number and appearance of the cells are looked at; in an embryo at the blastocyst stage, the level of expansion and the structure of the two different groups of cells are looked at. The assessment criteria are different in these two stages.

Can different grades be given to the same embryo?

This assessment depends largely on the observer. Two people looking at the same embryo, or even the same person at different times, may reach a different conclusion. For this reason you should read the grade not as a laboratory measurement value, but as a classification based on expert observation.

How is a day 3 embryo assessed?

On the second and third days after fertilisation, the embryo is at the cleavage stage. At this stage the following features are looked at:

• The number of cells
• Equality of the cells in size (symmetry)
• Fragmentation, that is, small pieces of cytoplasm left outside the cells
• Whether there is more than one nucleus in a single cell
• Early cleavage

According to guidelines on this subject, the number of cells and fragmentation are linked to live birth. Multinucleation has been linked to an abnormality in chromosome number (aneuploidy); however, the evidence on these associations is mostly limited. What early cleavage means has not yet been established with certainty. Laboratories may report these features with verbal expressions such as "little, moderate, much fragmentation" or with their own scoring systems.

How is a blastocyst (day 5–6) graded?

The embryo can reach the blastocyst stage on the fifth or sixth day. The Gardner system is widely used in assessing a blastocyst. In this system three elements are graded separately.

How are the letters and numbers in an embryo grade read?

• Expansion level: The number that shows how much the blastocyst has expanded.
• Inner cell mass: The cluster of cells in the inner part of the embryo, graded with a letter.
• Trophectoderm: The cells that form the outer layer, graded with a letter.

A grade such as "4AA" is therefore made up of three parts: the first number describes the level of expansion, and the next two letters describe the inner cell mass and the trophectoderm respectively. You can learn from your doctor or embryologist which appearance the letters correspond to, how the grade is written, and what information is included in the report.

According to the analyses conducted, the trophectoderm grade is the strongest predictor of live birth, followed by the expansion grade; the effect of the inner cell mass is less marked. It has also been reported that the live birth rate is lower in blastocysts that develop slowly.

Does a high embryo grade mean pregnancy?

There is a relationship between embryo grade and live birth, but this relationship is based on probability. An embryo with a high grade does not mean a pregnancy will occur; the predictive power of the grade is limited and does not determine your outcome. Alongside the embryo grade, your age, the conditions of your uterus and other factors also affect the outcome. For this reason you should read the grade neither as a promise of hope nor as a reason for hopelessness.

Does a good appearance show that the chromosomes are normal?

Although there is a relationship between appearance (morphology) and chromosome number, a grade based on appearance is not a chromosome diagnosis. For this reason a high grade does not mean that the chromosomes are normal. Tests that examine the genetic structure of the embryo (such as PGT-A) are completely separate methods from these; you can talk with your doctor about whether they will be considered for you.

Is a low grade a reason for transferring more than one embryo?

According to current guidelines on this subject, the decision on whether two embryos are transferred in a fresh transfer should not be based on embryo criteria or blastocyst quality. In frozen-thawed blastocysts too, single embryo transfer is recommended regardless of quality. That is, a low grade should not be used as a reason for "let's put two embryos in"; double embryo transfer increases the risk of multiple pregnancy. The number of embryos to be applied in Turkey is determined by current legislation and your doctor's assessment.

How should you assess it when your embryo grade is announced?

The grade of quality being high or low does not mean you know the outcome of treatment beforehand. For this reason, using the grade on its own as a decision criterion can mislead you. It is understandable to feel anxious when the grade is announced; do not hesitate to ask for support.

What questions can you ask your doctor and embryologist?

• On which day and at which stage were my embryos assessed?
• Which grading system is used at the centre, and how is my grade read?
• How much weight is this grade given when the decision about my transfer is made?
• What is planned for embryos with a low grade?
• Will genetic testing be considered for me?
• What information is in the report I was given?

Does grading carry a procedure risk for you?

The embryo assessment is done in the laboratory and carries no direct procedure risk for you. The real risk is a wrong expectation: seeing a high grade as an assurance, or a low grade as a definite outcome, can influence your decision process unnecessarily.